docs: def restrict_dates(feed: "Feed", dates: List[str]) -> List[str]:
      """
      Given a "Feed" and a date (YYYYMMDD string) or list of dates,
      coerce the date/dates into a list and drop the dates not in
      ``feed.get_dates()``, preserving the original order of ``dates``.
      Intended as a helper function.
      """
      # Coerce string to set
      if isinstance(dates, str):
          dates = [dates]
  
      # Restrict
      return [d for d in dates if d in feed.get_dates()]